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LASER DIAGNOSTICS AND SPECTROSCOPY
Nonlinear Polarization Rotation of Laser Radiation in Isotropic Media
S. Bakhramov, A. Kokhkharov, U. Makhmanov
Institute of Ion-Plasma and Laser Technologies named after U.A. Arifov, Uzbekistan Academy Sciences, Tashkent, Uzbekistan Main author email address: bahramov@mail.ru
This work discusses the nonlinear rotation of the polarization of laser radiation during propagation in atomic (alkali metal vapors - potassium, rubidium) and molecular (solutions of C70 fullerene) media. The observed self-induced optical anisotropy in atomic media is associated with the resonant nature of the nonlinear susceptibility and the finite degree of ellipticity of real laser radiation. The maximum values in the frequency dependence of the nonlinear rotation of the polarization of laser radiation were observed in the vicinity of resonant transitions.
Correlations between the processes of nonlinear rotation of the polarization ellipse of laser radiation passing through a solution of fullerenes and the synthesis of C70 fullerene nanoclusters are experimentally established. The experimental setup, the registration system, and the technique for measuring the nonlinear rotation of the polarization of laser radiation are given in [1].
Using the dynamic light scattering method on a ZetasizerNano ZEN3600 (Malvern Instruments Ltd.), the distribution of C70 fullerene nanoclusters over the hydrodynamic diameter and the formation of large stable nanoclusters were determined. It was found that a slight increase in the concentration of a fullerene solution is accompanied by an increase in the average diameter and the number of synthesized fullerene nanoclusters in solutions. For direct structural and dimensional studies of the kinetics of the formation of nuclei of C70 clusters in solutions, a transmission electron microscope (TEM microscope) with an ultrahigh resolution (~0.2nm) was used. The interaction of intense (I=0.52 MW/cm2) elliptically polarized laser radiation with a fullerene solution causes the appearance of a nonlinear effect in the solution. The dependence of the specific polarization rotation (asp) on the degree of radiation ellipticity (0) in a solution of C70 at two different concentrations in xylene was studied (Fig. 1). At a fixed intensity and degree of ellipticity of laser radiation, a gradual increase in the concentration of C70 in solution is accompanied by a decrease in the specific polarization rotation. The latter is associated with the tendency of C70 fullerene molecules to synthesize nanoclusters of various shapes and sizes in solution.
Fig. l.The dependence of the specific rotation of the elliptical polarization ap vs. the degree of ellipticity© of laser radiation in solutions of C70 in xylene at fullerene concentrations of -0.8 mg/mL (curve 1) and -1.2 mg/mL (curve 2).The peak intensity of laser pulses was -0.52 MW/cm2 at the wavelength of -532 nm.
Thus, a correlation has been found between the processes of formation of fullerene clusters in solutions and the value of the angles of the nonlinear rotation of the polarization ellipse of radiation passing through the solution. Using the obtained experimental data were determined the nonlinear addition to the refractive index in the studied media.
[1] Kokhkharov A.M., Zakhidov E.A., GofurovSh.P., Bakhramov S.A., Makhmanov U.K.,Clusterization of fullerene C70 molecules
in solutions and its influence to optical and nonlinear optical properties of solutions, International Journal of Nanoscience, Vol. 12, pp.1350027 (2013).
